This invention relates, generally, to the reduction of noise produced in a turbo-machine by the blades of a rotary ring of blades, either acting alone or in cooperation with the blades of a ring of stator vanes, and which blades generate a noise at their frequency of passage or, possibly, at a multiple of this frequency.
To reduce this noise, it has already been suggested to generate a kind of "counter-noise" at the same frequency of that to be reduced, but substantially opposed in phase to this latter.
One of the suggested solutions consisted in employing a secondary source of noise placed immediately adjacent the principal noise generator. By emitting a noise with an adequate frequency make-up and carefully selecting the amplitude and phase conditions, in certain sectors a reduction and even an obliteration of noise could be obtained by interference.
It has also been suggested to reproduce the noise of the rotor by injecting jets of pressurized fluid into the flow passage of the machine through orifices in one or a multiplicity of adjustable rings rotating with the rotor. The feeding of fluid should be done by way of the fan shaft.
None of these solutions has, however, provided a satisfactory result, either because their carrying out proved to be too complicated to be used in practice, or because the results obtained were too limited to compensate for the disadvantages arising from the installation of such a system.
Thus, the object of the invention is to obtain a better result together with a simplification of the method whereby the construction costs are more reasonable.